JP5523024B2 - Radiographic imaging method and apparatus - Google Patents

Description

  The present invention relates to a radiographic imaging method and apparatus, and more specifically, a long radiographic image representing the entire subject by combining a plurality of images obtained by sequentially radiographing a plurality of adjacent regions in a subject. The present invention relates to a radiographic imaging method and apparatus.

  2. Description of the Related Art Conventionally, there are known devices that detect radiation such as X-rays through a subject and obtain a radiation image representing the subject.

  As such a radiation detector used in the apparatus, an FPD (Flat Panel Detector) is known. The FPD detects radiation that has passed through a subject, converts it into an electrical signal, and outputs an image signal representing a radiation image of the subject. A radiographic imaging apparatus using this FPD can output an image signal representing a radiographic image of a subject immediately after radiography (several seconds later).

  Further, radiation imaging is performed by sequentially moving the FPD to a plurality of adjacent regions in the subject, and a long radiation image representing the entire subject, for example, the entire spine, is synthesized by combining a plurality of images obtained by each radiation imaging. 2. Description of the Related Art Radiographic imaging devices that obtain images and whole lower limb images are known.

  In such radiography for obtaining a long radiographic image, the position of the radiation source is fixed, and the direction of the radiation source is directed toward the FPD for each radiography while sequentially moving one FPD. A method of setting and performing each radiography is known. That is, a method is known in which each radiographing is performed by directing a specific range in the radiation range of radiation emitted from a radiation source toward the FPD.

  In this method, for example, every time radiographing is performed by sequentially moving the FPD, the radiation center of the radiation source passes through the center of the FPD so that the radiation center axis passing through the center of the radiation range of radiation emitted from the tube of the radiation source passes through the center of the FPD. What is performed by determining the position and orientation is known.

  There is also known a method of performing each radiography while sequentially moving the position of the radiation source and the position of the FPD relative to the position of the subject, that is, without changing the relative positional relationship between the radiation source and the FPD. ing.

  By the way, the radiation emitted from the radiation source has a higher intensity on the cathode side of the tube than on the anode side, so that the intensity is asymmetric with respect to the radiation center axis that is the boundary between the cathode side and the anode side. Have a distribution. The phenomenon in which such an asymmetric intensity distribution occurs is called a heel effect.

  Irradiation unevenness due to such an intensity distribution is also observed in radiation irradiated in each radiography for obtaining a long radiation image. Therefore, for example, a density distribution is generated from the upper edge portion to the lower edge portion of each image obtained by each radiography when obtaining a radiation image that is long in the vertical direction. As a result, for example, a density difference occurs between the lower edge of a specific image obtained by radiography and the upper edge of another image adjacent to the lower side of the specific image, so that the specific image is adjacent. A density step (hereinafter referred to as a density step) may occur at the boundary with another image.

  That is, when a plurality of images obtained by radiography are combined to obtain a long radiation image representing the entire subject, a density step may occur at the joint between the combined images.

  In such a case, for example, a method of suppressing such a density step by image processing using correction data obtained by separately performing radiography for correcting the density step (see Patent Document 1) is known. It has been. Further, for example, from the experience value possessed by a radiographer or the like, the distance from the upper edge portion to the lower edge portion of the region to be imaged in one radiography is shortened, that is, the length of each region in the subject. It is also conceivable to suppress the density difference by performing radiography while setting the width (imaging width) in the scale direction to be small.

JP 2006-141905 A

  However, the method of correcting the density difference by image processing has a problem that the radiographic imaging for obtaining the correction data is separately performed, so that the imaging burden increases. In addition, in the method of changing the radiography setting depending on the experience value possessed by a radiographer or the like, the density difference between the images at the joint is set to a desired level or less (the density difference between the images at the joint is sufficiently reduced). It may not be possible to make it inconspicuous.

  For this reason, there is a demand for making the density step generated at the joint between the synthesized images less noticeable without increasing the burden of radiography when acquiring a long radiation image.

  The present invention has been made in view of the above circumstances, and provides a radiographic imaging method and apparatus capable of easily acquiring a high-quality long radiographic image in which the density difference in the joints is inconspicuous. It is intended.

  The radiographic imaging device of the present invention combines a plurality of images obtained by sequentially radiographing a plurality of adjacent areas in a subject using the same radiation source and the same radiation image detector. A radiographic imaging device that obtains a long radiographic image representing the whole of the radiographic image, and radiographing condition acquisition means for acquiring radiographing conditions when performing radiographic imaging, and a radiographable width in the longitudinal direction in each radiographic imaging An imaging range acquisition unit that is obtained from conditions, and an allocation unit that allocates a plurality of areas in the subject to be radiographed so that the longitudinal imaging width of each radiography is equal to or less than the imaging range. It is characterized by comprising.

  This radiographic imaging device combines a plurality of images obtained by sequentially radiographing a plurality of adjacent areas in a subject using the same radiation source and the same radiographic image detector, and the entire subject. A radiographic imaging device that obtains a long radiographic image representing imaging conditions, an imaging condition acquisition means for acquiring imaging conditions when performing radiography, and a long radiograph obtained by the sequential radiography under the imaging conditions Regarding the radiographic image, the radiographic imaging is used to determine the radiographable width in the longitudinal direction in each radiography so that a density step due to the heel effect does not appear at the joint between the images constituting the long radiographic image. The imaging range acquisition means obtained from the imaging conditions corresponding to the above, and the imaging width in the longitudinal direction in each radiation imaging is equal to or less than the imaging possible width corresponding to the radiation imaging It can be provided with a allocation means for performing allocation of a plurality of regions in the subject to be photographed subject ray imaging.

  The imaging condition can be an imaging distance, a dose of radiation emitted from a radiation source, a focal point size of a tube of the radiation source, or a material of a tube target of the radiation source.

  The photographing range acquisition means obtains a photographing width when a radiation bundle portion having the smallest irradiation unevenness due to the heel effect is irradiated to each region in the subject among radiation bundles emitted from a tube of a radiation source. It is desirable to do.

  The radiographic imaging apparatus preferably includes a tube swinging means for changing the direction of the tube of the radiation source to the long direction.

  The radiographic image capturing method of the present invention combines a plurality of images obtained by sequentially radiographing a plurality of adjacent regions in a subject using the same radiation source and the same radiation image detector. A radiographic imaging method for obtaining a long radiographic image representing the whole of the radiographing method, acquiring radiographing conditions when radiography is performed, obtaining a radiographable width in the longitudinal direction in each radiography from the radiographing conditions, A plurality of areas in the subject to be imaged in the radiation imaging are allocated so that the imaging width in the longitudinal direction in imaging is equal to or less than the imaging possible width.

  This radiographic imaging method uses the same radiation source and the same radiographic image detector to synthesize a plurality of images obtained by sequentially radiographing a plurality of adjacent areas in a subject, and thereby the entire subject. A radiographic image capturing method for obtaining a long radiographic image representing a radiographic image obtained by acquiring radiographing conditions when performing radiography, and for a long radiographic image obtained by the sequential radiography under the radiographing conditions, An imaging condition corresponding to the radiography for the radiographable width in the longitudinal direction in each radiography so that a density step due to the heel effect does not appear at the joint between the images constituting the long radiographic image The plurality of regions in the subject to be imaged in the radiography so that the imaging width in the longitudinal direction in each radiography is equal to or less than the imageable width corresponding to the radiography It can be made to carry out the assignment.

  According to the radiographic imaging method and apparatus of the present invention, the imaging conditions for each radiography are acquired, the imageable width in the longitudinal direction for each radiography is obtained from the imaging conditions, and the imaging in the longitudinal direction is performed for each radiography. Since the allocation of a plurality of areas in the subject to be imaged so that the width is equal to or less than the above imageable width, the density step at the joint of each image constituting the long radiographic image is inconspicuous, A long radiation image with high quality can be easily acquired.

  That is, it is possible to accurately predict the intensity distribution of the radiation applied to the subject from predetermined imaging conditions, and the joints between the images constituting the long radiographic image obtained by sequential radiography under the predetermined imaging conditions Therefore, it is possible to accurately obtain the imageable width in the longitudinal direction for each radiation imaging so as to prevent the density step due to the heel effect from appearing from the imaging conditions corresponding to the radiation imaging. Then, each radiographing is performed so that the radiographing width in each radiography is equal to or less than the radiographable width corresponding to the radiographing, whereby image processing and the like are separately performed on each image constituting the long radiographic image. Without applying the density step, it is possible to make the density step generated at the joint of each image inconspicuous to a desired level or less.

  In addition, if the imaging condition is the imaging distance, the dose of radiation emitted from the radiation source, the focal point size of the tube, or the material of the tube target, the longitudinal direction for each radiographing It is possible to more reliably determine the imageable width.

  Further, the imageable range acquisition means obtains the imageable width when each region in the subject is irradiated with the radiation bundle portion having the smallest irradiation unevenness due to the heel effect among the radiation bundles emitted from the tube of the radiation source. By so doing, it is possible to more reliably acquire a long radiation image in which the density step at the joint of each image is inconspicuous.

  Furthermore, if a tube swinging means for changing the direction of the tube of the radiation source to the long direction is provided, a long radiation image in which the density step of the joint of each image is more inconspicuous can be obtained. Can be acquired.

  In addition, if the imaging width is determined to be the largest within the range of the imaging possible width, the number of imaging for obtaining a long radiographic image without increasing the area to be imaged unnecessarily is increased. The radiography can be performed efficiently.

The figure which shows schematic structure of the radiographic imaging apparatus by embodiment of this invention Diagram showing the state of radiation emitted from a tube target The figure which shows the radiation intensity distribution of the area which received the radiation from the tube target The figure which shows the difference of the size of the irradiation non-uniformity due to the difference in the focal point size of the tube The figure which shows the difference in the size of the unevenness of irradiation due to the difference in the material of the tube target The figure which shows the radiation intensity distribution irradiated on a radiation detection surface in 4 times imaging | photography The figure which shows the radiation intensity distribution irradiated on the radiation detection surface in 3 times imaging | photography The figure which shows the radiation intensity distribution irradiated on the radiation detection surface in one imaging | photography. The figure which shows a mode that the long radiographic image obtained by four times of radiography was compared with the long radiographic image obtained by three times of radiography A diagram showing the intensity distribution when a radiation bundle emitted from a tube is detected with the center axis of radiation orthogonal to the detection surface Diagram showing the intensity distribution when a radiation bundle emitted from a tube is detected with the radiation center axis inclined with respect to the detection surface

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing a schematic configuration showing an example of a radiographic image capturing apparatus for carrying out a radiographic image capturing method according to an embodiment of the present invention.

  A radiographic image capturing apparatus 100 of the present invention shown in FIG. 1 sequentially uses a single radiation source 10 and a single radiographic image detector 15 to sequentially form a plurality of adjacent areas M1, M2,. A plurality of images obtained by radiography are combined to obtain a long radiation image representing the entire subject M.

  The radiographic image capturing apparatus 100 configures a long radiographic image for a radiological image acquisition unit 82 that acquires radiographic imaging conditions and a long radiographic image obtained by sequential radiographic imaging under the radiographic conditions. Corresponding to the radiographing, the radiographable width in the long direction (arrow Y direction in the figure) for each radiographing to prevent density step due to the heel effect from appearing at the joint (boundary) between each image And a radiographable width acquisition unit 84 obtained from the radiographing conditions, and the radiographic imaging subject M so that the radiographic width of each radiographing is equal to or smaller than the radiographable width corresponding to the radiographic imaging. And an allocation unit 86 that performs allocation (frame allocation) of the plurality of areas M1, M2,.

  The imaging condition acquisition unit 82 acquires imaging distance data, acquisition of radiation dose data emitted from the radiation source 10 as a radiographic imaging condition, and the focal size of the tube 10K of the radiation source 10. Or data indicating the material of the tube target disposed in the radiation source 10 is acquired.

  The radiographic imaging device 100 includes a radiation source 10 that emits radiation H, a radiation image detector 15 that detects the radiation H, a detector moving unit 20 that moves the radiation image detector 15 along the subject M, and radiation. And a radiation source placement unit 25 for placing the source 10. The radiation image detector 15 has a radiation detection surface 16 that receives the radiation H emitted from the radiation source 10 and passed through the subject M and detects the intensity distribution of the radiation H.

  The radiation image detector 15 can employ an FPD (Flat Panel Detector) that detects radiation transmitted through the subject M, converts it into an electrical signal, and outputs image data representing the radiation image of the subject M. This FPD can output image data representing a radiographic image of the subject M immediately after radiography (several seconds later).

  The detector moving unit 20 holds the radiation image detector 15 between the two support columns 21 rising from the floor surface 5F in the vertical direction (arrow Y direction in the figure), and the radiation image detector 15 is moved in the long direction. A moving mechanism 22 for moving in a vertical direction (vertical direction) in which a certain column 21 extends is provided. The moving mechanism 22 can support the radiation image detector 15 with a conventionally known linear slide mechanism or the like and move it using a driving source such as a motor.

  When performing radiography to acquire a long radiographic image, the subject M is arranged along the moving direction of the radiographic image detector 15 (along the arrow Y direction in the figure). That is, each radiographing is performed with the subject M standing on the floor.

  The radiation source arrangement unit 25 holds and moves the radiation source 10 so as to face the radiation detection surface 16 of the radiation image detector 15 with the subject M interposed therebetween (so as to face in the arrow Z direction in the figure). It is. The radiation source arrangement unit 25 includes a column 26 extending in a vertical direction from the ceiling 5E, a ceiling base table 27 that moves the column 26 in the opposite direction along the ceiling 5E (in the direction of arrow Z in the figure), and a column 26 Can be moved in the vertical direction (in the direction of arrow Y in the figure) and around an axis perpendicular to the paper surface (an axis parallel to the X-axis perpendicular to the YZ plane in the figure) And a rotatable turntable 28.

  The radiation source 10 is arranged on the turntable 28, and the radiation source 10 can be moved in the vertical direction (arrow Y direction in the figure) and the horizontal direction (arrow Z direction in the figure) by the radiation source placement unit 25. In addition, it can be rotated through a turntable 28 around an axis parallel to the X axis in the drawing passing through the approximate center of the radiation source 10.

  Further, the tube swinging portion 19 changes the direction of the tube 10K disposed in the radiation source 10 along the long direction (the arrow Y direction in the figure). Here, the tube swing unit 19 changes the direction of the tube 10K relative to the radiation source 10 main body.

  The mechanism for operating the radiation source arrangement unit 25 and the tube swinging unit 19 can be formed using a conventionally known linear slide mechanism, rotation mechanism, and drive source such as a motor.

  In addition, the radiographic image capturing apparatus 100 uses the detector moving unit 20 to perform radiographic imaging of the radiographic image detector 15 along the direction in which the subject M extends (longitudinal direction). The radiation source 10 is arranged by the radiation source arrangement unit 25 so that the irradiation direction of the radiation H emitted from the radiation source 10 faces the direction of the radiation detection surface 16 at each sequentially moved position. A long imaging control unit 88 that controls radiography of adjacent areas M1, M2,... In the subject M for each position and the respective image portions obtained for each radiography are synthesized. An image composition unit 35 for obtaining a long radiation image representing the entire subject M and a display 60 for displaying the long radiation image synthesized by the image composition unit 35 are provided.

  The allocating unit 86 that allocates a plurality of areas M1, M2,... In the subject M to be imaged is input with photographic width information J2 indicating a photographic possible width from the photographic possible width acquisition unit 84, and photographic. Imaging condition information J1 indicating imaging conditions is input from the condition acquisition unit 82, and the imaging width and imaging position P1 at the time of each radiography so that a long radiographic image in which the joints of the image portions are not conspicuous can be obtained. Assignment information J3 for assigning P2.

  Note that the allocation unit 86 may receive the shooting condition information J1 and the shooting width information J2 from the shooting available width acquisition unit 84.

  Here, the allocation information J3 output from the allocation unit 86 is input to the long imaging control unit 88, and the long imaging control unit 88 determines the position of the radiation source 10 for each radiography based on the allocation information J3. Each part is controlled so as to determine the position and the position of the radiation detector 15 and the like.

  The long imaging control unit 88 receives data regarding the imaging width and imaging position at the time of each radiography from the allocation unit 86, and the tube 10K of the radiation source 10 according to the imaging width and imaging position. It also controls the direction of the.

  Note that subject information regarding the subject M and imaging conditions for obtaining a long radiographic image are input to the console 70, and such information is output to the imaging condition acquisition unit 82, the long imaging control unit 88, and the like.

  Further, the overall operation of the radiographic image capturing apparatus 100 that performs long radiography and the timing of each operation are controlled by the console 70. The imaging condition acquisition unit 82, the imageable width acquisition unit 84, the allocation unit 86, the long imaging control unit 88, the image composition unit 35, and the like may be arranged in the console 70.

<Irradiation unevenness due to heel effect>
FIG. 2 shows the inside of a tube 10 </ b> K that emits radiation arranged in the radiation source 10, and shows the state of radiation emitted from the tube target Tr that has been irradiated with electrons by the electron gun Er. . FIG. 3 shows a region on the detection surface where the radiation is detected on the horizontal axis R and a coordinate axis that defines the intensity of the detected radiation on the vertical axis E on the region irradiated with radiation emitted from the tube target Tr. It is a figure which shows intensity distribution.

  As shown in FIG. 2, the radiation bundle φH emitted from the tube target Tr irradiated with electrons by the electron gun Er, that is, the tube 10K of the radiation source 10, is a radiation center axis passing through the center of the radiation bundle φH. The radiation range is expanded radially around Cr, and the detection surface Sr is irradiated. The position R4 is a position on the detection surface Sr that intersects the radiation center axis Cr. Positions R3, R2, and R1 at which the radiation reaches the side of the arrow − direction on the detection surface Sr around the position R4 are shown at equal intervals, and the radiation reaches the side of the arrow + direction in the figure. Positions R5, R6, R7 are shown at equal intervals.

  As an example of the intensity of radiation detected on the detection surface Sr, for example, assuming that the radiation intensity detected at a position R4 on the radiation center axis Cr is a value 100 (unit is omitted), the cathode side in the direction indicated by the arrow in FIG. At the positions R3, R2, and R1, the values are 103, 105, and 95, respectively. On the other hand, values 85, 73, and 31 are respectively obtained at positions R5, R6, and R7 on the anode side in the arrow + direction in the figure.

3 plots the radiation intensity at each of the positions R1 to R7, and shows an outline of the intensity distribution of the radiation irradiated on the detection surface Sr. As shown in FIGS. The radiation bundle φH radiated from the light has an asymmetric intensity distribution with respect to the radiation center axis Cr. Irradiation unevenness of the radiation bundle φH is caused by the heel effect. This heel effect is due to the fact that the intensity of radiation on the cathode side (arrow-direction side in the figure, position R1 side) of the tube is greater than on the anode side (arrow + direction side, position R7 side in the figure). This produces an asymmetric intensity distribution in which increases. The radial center axis Cr is located at the boundary between the cathode side and the anode side.

  Here, the radiation reaching the position R7 has a longer distance when passing through the tube target Tr than the radiation reaching the position R1, and the absorption of the radiation is larger, so that the radiation reaching the position R1 is larger. Indicates attenuation of radiation intensity.

  Note that the magnitude of the radiation irradiation unevenness due to the heel effect is, for example, the radiation intensity between the position R1 and the position R7 when the range where the irradiation unevenness is detected is the range from the position R1 to the position R7 on the detection surface Sr. (Value 95−value 31 = value 64).

<Difference in shootable range due to difference in tube focus size>
FIG. 4 shows the irradiation on the detection plane where the radiation is detected on the horizontal axis R, and the irradiation of the radiation due to the heel effect caused by the difference in the focal spot size of the tube on the coordinate axis indicating the intensity of the detected radiation on the vertical axis E. It is the figure which showed the difference in the magnitude | size of nonuniformity. In the same manner as described above, the radiation intensity at each position is shown with the radiation intensity at the radiation center axis Cr being 100.

  As shown in FIG. 4, the attenuation of the radiation intensity in the region on the anode side (the arrow + direction side in the figure) that has been irradiated with radiation emitted from the tube Kb having a large focal size is the tube Ks having a small focal size. This is smaller than the attenuation of the radiation intensity in the region on the anode side (the side in the arrow + direction in the figure) that has been irradiated with the radiation emitted from. On the other hand, in the region on the cathode side (the arrow + direction side in the figure), the radiation intensity is substantially constant regardless of the focal spot size. That is, the irradiation unevenness of the tube Kb having a large focal size is smaller than the irradiation unevenness of the tube Ks having a small focal size.

  Accordingly, regarding the focal size of the tube, which is an imaging condition, the radiation unevenness due to the heel effect increases as the focal size of the tube decreases. Therefore, the imageable width acquisition unit 84 performs imaging as the focal size of the tube decreases. Decrease the possible width.

<Difference in shootable range due to difference in tube target material>
FIG. 5 shows the irradiation on the detection surface where radiation is detected on the horizontal axis R and the coordinate axis indicating the intensity of the detected radiation on the vertical axis E, and radiation irradiation due to the heel effect resulting from the difference in the material of the tube target. It is the figure which showed the difference in the magnitude | size of nonuniformity. FIG. 5 shows the radiation intensity at each position with the radiation intensity at the radiation center axis Cr as a value 100 as described above.

  As shown in the figure, the attenuation of the radiation intensity Mo on the anode side (the arrow + direction side in the figure) of the radiation emitted from the radiation source using the molybdenum material for the tube target is the radiation using the tungsten material for the tube target. It is larger than the attenuation of the radiation intensity W on the anode side (the arrow + direction side in the figure) of the radiation emitted from the source. On the other hand, on the cathode side (the arrow + direction side in the figure), the radiation intensity is substantially constant regardless of the difference in the tube target.

  Therefore, regarding the material of the tube target of the radiation source, which is the imaging condition, when using the radiation bundle on the anode side, the imageable width acquisition unit 84 determines the size of the imageable width when tungsten is applied to the tube target. Is determined to be smaller than the width of the imageable width when molybdenum is applied to the tube target. Further, when using the cathode-side radiation bundle, the imageable width acquisition unit 84 sets the imageable width when tungsten is applied to the tube target and the imageable width when molybdenum is applied to the tube target. Set the size to the same size.

<Differences in coverage due to differences in radiation dose>
Regarding the radiation dose emitted from the radiation source that is the imaging condition, the greater the radiation dose, the greater the radiation unevenness due to the heel effect, so the imageable width acquisition unit 84 can perform the imaging as the radiation dose increases. Decrease the width.

  That is, for example, even if the tube voltage changes and the dose of radiation emitted from the radiation source varies, the radiation intensity distribution when this radiation is detected by the radiation detector hardly varies. However, when two types of images obtained using radiations with different doses are compared visually, the contrast of the images obtained by irradiation with large doses of radiation increases, and The contrast of the image obtained by irradiation is lower than the contrast of the image obtained by receiving the large dose. Therefore, the imageable width acquisition unit 84 determines the imageable width as the dose of radiation emitted from the radiation source increases.

<Difference in shootable range due to difference in shooting distance>
Regarding the shooting distance that is the shooting condition, the shootable width acquisition unit 84 sets the shootable width to be smaller as the shooting distance is smaller and to be larger as the shooting distance is larger.

  Next, the operation of the radiographic image capturing apparatus 100 will be described.

  Here, first, the direction of the tube 10K, that is, the tube, is such that the radiation center axis Cr of the radiation emitted from the tube 10K of the radiation source 10 passes through the center of the imaging width in the longitudinal direction at the time of each radiography. A case where radiation imaging is performed with the direction of the radiation bundle φH emitted from the sphere 10K being determined will be described. Then, in the latter half, the tube so that the position through which the radial center axis Cr passes is removed from the center of the imaging width in the longitudinal direction at the time of each radiography so that the size of the irradiation unevenness due to the heel effect is reduced. A case where the direction of 10K, that is, the direction of the radiation bundle φH emitted from the tube 10K is determined will be described.

<Initial settings for radiation imaging>
The console 70 stores in advance an initial setting for acquiring a standard long radiation image. In this initial setting, a long radiographic image is acquired by three radiographs, and the radiation center axis Cr of the radiation emitted from the tube 10K of the radiation source 10 is in the long direction at the time of each radiographing. Radiation imaging is performed with the orientation of the tube 10K so as to pass through the center of the imaging width.

  That is, in this initial setting, the tube 10K has an irradiation width of the cathode-side radiation bundle that matches the irradiation width of the anode-side radiation bundle within the range of the imaging width in the longitudinal direction at the time of each radiography. Radiation imaging is performed with the orientation determined.

<Radiography taking into account variations in unevenness of irradiation due to the heel effect>
The console 70 is operated to input subject information, which is information related to the subject M, and imaging conditions in radiation imaging for obtaining a long radiation image. Subject information, shooting conditions, and the like input to the console 70 are transferred to and input to the shooting condition acquisition unit 82 and the long shooting control unit 88.

  The imageable width acquisition unit 84 uses the imaging conditions acquired by the imaging condition acquisition unit 82 to determine the size of the radiation unevenness due to the heel effect when the radiation emitted from the radiation source 10 is applied to the radiation detection surface 16. The imageable width in the longitudinal direction is taken into consideration.

  More specifically, the radiographable width acquisition unit 84 has a long radiographic image obtained by sequential radiography under the above radiographing conditions, at a joint (boundary) between each image constituting the long radiographic image. In order to prevent the density step due to the heel effect from appearing, the imageable width in the longitudinal direction for each radiation imaging is obtained from the imaging conditions.

  That is, for a long radiographic image obtained by sequential radiography under the above imaging conditions, the density difference due to the heel effect occurring at the joint (boundary) between each image constituting the long radiographic image is less than or equal to a predetermined value. In order to be (not conspicuous), the imageable width in the longitudinal direction for each radiation imaging is obtained from the imaging conditions.

  The allocating unit 86 receives the radiation so that the imaging width in the longitudinal direction in each radiation imaging is equal to or less than the imaging possible width based on the input information indicating the imaging possible width obtained by the imaging possible width acquisition unit 84. A plurality of areas M1, M2,... In the subject M to be photographed are assigned.

  The shootable width acquisition unit 84 has a predetermined size or less so that the irradiation unevenness of the radiation emitted from the tube K10 and irradiated on each region in the subject M under the input shooting conditions is less conspicuous in the density step. Thus, the imaging width in each radiography is determined.

  Here, the image-capable width in the longitudinal direction determined by the image-capturable width acquisition unit 84 is smaller than the image-capable width in the longitudinal direction at the initial setting. The allocating unit 86 assigns an imaging area corresponding to each area in the subject M (frame) so that a long radiographic image can be obtained by four radiographic imagings by reducing the imaging width in the longitudinal direction in each radiographic imaging. Allocation).

  The long imaging control unit 88 inputs the allocation data created by the allocation unit 86, and the imaging width and imaging in the longitudinal direction in each radiography so that a long radiographic image can be obtained by four times of radiography. In order to determine the position, the arrangement of the radiation source 10 and the tube 10K for each radiographing, the position of the radiation image detector 15, and the like are controlled.

  More specifically, the long photographing control unit 88 obtains a long radiographic image from the console 70 or the allocating unit 86 by four times of radiography, the photographing width in the long direction, the photographing position, and the photographing region. , The ratio of the cathode-side radiation bundle to the anode-side radiation bundle in each radiographing, etc. are input, and the detector moving unit 20, the radiation source arranging unit 25, the tube swinging unit 19, the image combining unit 35, etc. To control.

  Each region M1... M in the subject M obtained by the control of the long photographing control unit 88 is obtained. Each image indicating M2... And the information related to radiography output from the long imaging control unit 88 are input to the image synthesis unit 35, and the image synthesis unit 35 synthesizes each image to generate a long radiographic image. Form. The long radiation image synthesized by the image synthesis unit 35 is displayed on the display device 60.

  In addition, regarding the imageable width in the longitudinal direction obtained by the imageable width acquisition unit 84, image data obtained by radiation imaging under some imaging conditions (image data indicating a density distribution caused by the heel effect) May be stored and obtained using these image data. For example, a plurality of information that may be obtained by acquiring and storing information indicating the density distribution of a blank image obtained when there is no object to be imaged under various imaging conditions and actually performing sequential radiography. JND value (Just Noticeable Difference) of adjacent pixel values with a joint (image boundary) between the images as a target (image region where there is no object to be imaged) The width in the longitudinal direction where the difference value of (index) is less than or equal to a certain value may be obtained as the imageable width. Here, “below a certain value” is considered to be set so that the difference between the JND values of adjacent pixel values sandwiching the joint between two images is within 0.01, for example. It is done.

  For example, Re-W (alloy doped with rhenium in tungsten) is used as the material of the tube target, the spread angle of the radiation emitted from the tube (tube focus size) is 12 degrees, and the shooting distance is 100 cm. Irradiation unevenness due to the heel effect can be suppressed to a desired level or less by performing each radiographing by setting the imageable width to 20 cm (30 mm when the imaging distance is 120 cm).

<Irradiation unevenness in long radiography>
Hereinafter, radiation irradiation unevenness due to the heel effect when performing long radiation imaging will be described. Here, a case will be described in which each radiation imaging is performed through a transparent subject having a radiation transmittance of 100%.

  FIG. 6 shows the intensity distribution of radiation applied to the entire subject when a long radiographic image is obtained by four radiographs on the coordinates indicating the radiation intensity on the vertical axis E and the position in the longitudinal direction on the horizontal axis Y. It is a figure which shows f1. This figure shows radiation irradiation unevenness when a long radiation image is obtained by four times of radiography in accordance with the change of the imaging conditions.

  FIG. 7 shows the intensity distribution of radiation applied to the entire subject when a long radiographic image is obtained by three radiographs on the coordinates indicating the radiation intensity on the vertical axis E and the position in the longitudinal direction on the horizontal axis Y. It is a figure which shows f2. This FIG. 7 shows that a long radiographic image is obtained by the same three radiography as the initial setting, even though the irradiation unevenness due to the heel effect is larger than the irradiation unevenness in the initial setting due to the change of the imaging condition. It shows the radiation unevenness of radiation when trying to obtain.

  FIG. 8 is a diagram showing the intensity distribution fe of the radiation irradiated on the radiation detection surface by one radiography on the coordinates indicating the radiation intensity on the vertical axis E and the position in the longitudinal direction on the horizontal axis Y. This figure shows how the size of radiation irradiation unevenness changes according to the setting of the use range in the intensity distribution fe of radiation irradiated in one imaging, that is, in accordance with the imaging width when each radiography is performed. This shows how the size of radiation irradiation unevenness varies.

  As shown in FIG. 7, the intensity distribution of the radiation used to acquire each image portion G2 (see FIG. 9 described later) in the three radiographs is substantially the same in each radiograph, and the radiation intensity distribution due to the heel effect Due to the asymmetry, an intensity distribution step (intensity distribution step size δ2) occurs at the radiation detection position K2 corresponding to the joint (boundary) of each image portion G2.

  On the other hand, as shown in FIG. 6, the radiation intensity distributions used for obtaining each image portion G1 (see FIG. 9 described later) in the four radiographs also substantially coincide with each other, and the radiation due to the heel effect Due to the asymmetry of the intensity distribution, an intensity distribution step (intensity distribution step size δ1) slightly occurs at the radiation detection position K1 corresponding to the joint (boundary) of each image portion G1. That is, the step size δ1 generated in the intensity distribution f1 of the radiation irradiated to each imaging region when a long radiographic image is obtained by four radiographs is a long radiographic image by three radiographs. Is smaller than the step size δ2 generated in the intensity distribution f2 of the radiation irradiated to each imaging region (δ1 <δ2).

  As shown in FIG. 8, the radiation emitted from the radiation source at each of the four radiographs and the radiation emitted from the radiation source at each of the three radiographs both show the intensity distribution fe of the radiation. Although a partial area in the radiation is used, the size of the radiation unevenness due to the heel effect is changed by changing the area in the radiation intensity distribution fe used to obtain the image portions (G1, G2). Is fluctuating.

  That is, the region in the radiation intensity distribution fe used in each of the three radiographs is a region indicated by the symbol W1 in the figure, and the magnitude of radiation irradiation unevenness due to the heel effect is the radiation intensity at both ends of the region W1. The difference value α1 is indicated. On the other hand, the region in the radiation intensity distribution fe used in each of the four times of radiography is a range narrower than the above range W1 as indicated by the symbol W2 in the figure, and the size of the irradiation unevenness is at both ends of this region W2. It is indicated by a value α2 (α2 <α1) of the difference in radiation intensity.

  FIG. 9 is a diagram showing a state in which a long radiation image obtained by four times of radiography and a long radiographic image obtained by three times of radiography are compared.

  As shown in FIG. 9, a long radiation image GG1 obtained by synthesizing four narrow image portions obtained by four times of radiography has a width obtained by three times of radiography. The density step generated at the joint (boundary) between adjacent image portions can be made smaller than the long radiation image GG2 obtained by combining the three wide image portions.

  In the above description with reference to FIG. 8, by reducing the area W1 in the radiation intensity distribution fe used in radiography to the area W2 (that is, by reducing the imaging width in the longitudinal direction), It was shown that the radiation unevenness due to the heel effect can be reduced (α2 <α1). However, even if the size of the region in the radiation intensity distribution fe used in radiography is the same (that is, the imaging width in the longitudinal direction is the same), the variation in the radiation intensity distribution fe is smaller. The use of the region, for example, the region W3, can further reduce the size of the radiation unevenness (α3 <α2 <α1). However, in such a case, the position of the radiation center axis Cr is located in a region off the center in the longitudinal direction of the range of the imaging width of each radiography, that is, the radiographic imaging width of each radiography. It will be located off the center.

  More specifically, the region W3 in the radiation bundle is determined so that the irradiation range of the radiation bundle on the cathode side is larger than the irradiation range of the radiation bundle on the anode side. Irradiation unevenness due to the heel effect in the region W3 can be reduced as the area is larger than the irradiation range of the radiation bundle on the anode side.

  As described above, in order to make the joints of the image portions constituting the long radiation image inconspicuous, within the imaging width range of each radiography, the irradiation range of the radiation bundle on the cathode side is that of the radiation bundle on the anode side. It is desirable to determine the direction of the tube 10K so as to be larger than the irradiation range so that each radiographing is performed.

  That is, when performing radiography to obtain a long radiographic image by the radiographic imaging device 100, each of the radiographing condition acquisition unit 82, the radiographable width acquisition unit 84, the allocation unit 86, the long radiography control unit 88, and the like. The operation is such that each region M1, M2,... In the subject M irradiated with radiation in each radiography has a tube so that the irradiation range of the radiation bundle on the cathode side is larger than the irradiation range of the radiation bundle on the anode side. It is desirable to assume that the orientation of the sphere 10K is determined.

  The ratio of the irradiation range of the cathode side radiation bundle to the irradiation range of the anode side radiation bundle may be automatically determined by the controller 70 so that the ratio of the cathode side radiation bundle is maximized, for example. The ratio may be input to the controller 70 by the operator.

  Hereinafter, when the ratio of the irradiation range of the radiation bundle on the cathode side and the irradiation range of the radiation bundle on the anode side is equal, the irradiation range of the radiation bundle on the cathode side is larger than the irradiation range of the radiation bundle on the anode side. Compare with the set case.

  FIG. 10A is a diagram showing an intensity distribution when a radiation bundle emitted from a tube is detected in a state where the radiation center axis is orthogonal to the detection surface. That is, FIG. 10A is a diagram showing a state in which the radiation bundle φH is irradiated from the tube 10K so that the position of the radiation center axis Cr is positioned at the center of the width of the detection surface Sr of the radiation image detector 15. .

  FIG. 10B is a diagram showing an intensity distribution when a radiation bundle emitted from a tube is detected in a state where the radiation center axis is inclined with respect to the detection surface. That is, in FIG. 10B, the radiation bundle φH is irradiated by changing the direction of the tube 10K so that the position of the radiation center axis Cr is located at a position deviated from the center of the width of the detection surface Sr of the radiation image detector 15. The radiation center axis Cr is positioned so that the irradiation range of the radiation bundle on the cathode side is larger than the irradiation range of the radiation bundle on the anode side within the imaging width range of the radiography. It is a figure which shows the mode of time.

  10A and 10B, the radiation bundle φH emitted from the tube 10K of the radiation source 10 is along the detection surface Sr of the radiation image detector 15 (along the moving direction of the radiation image detector 15). (B) shows the state of irradiation on the region SSr.

  The upper graphs in FIGS. 10A and 10B are coordinate axes indicating the position on the region SSr along the detection surface Sr of the radiation image detector 15 on the horizontal axis R, and the intensity of the radiation irradiated on the region SSr on the vertical axis E. The figure shows the intensity distribution fe of the radiation bundle φH emitted from the tube 10K and irradiated onto the region SSr.

  Here, for each of FIGS. 10A and 10B, the position on the region SSr irradiated with the radiation bundle φH on the lower region SSr is on the horizontal axis R in the intensity distribution fe shown in the upper graph in FIGS. 10A and 10B. Corresponds to the position of.

  As shown in FIG. 10A, when the radiation center axis Cr is positioned at the center of the width of the detection surface Sr of the radiation image detector 15 and the radiation bundle φH is irradiated onto the region SSr, the detection surface Sr of the radiation image detector 15 is irradiated. Is irradiated with a radiation bundle portion φHAp which is a part of the radiation bundle φH. The radiation intensity distribution in the radiation bundle portion φHAp is not constant due to the influence of the heel effect, and is biased as shown in FIG. 10A. That is, the intensity distribution of the radiation bundle is substantially constant from the center of the detection surface Sr (radiation center axis Cr) to the cathode side, but as the distance from the center of the detection surface Sr (radiation center axis Cr) to the anode side increases. The intensity is monotonously decreasing.

  On the other hand, as shown in FIG. 10B, the position of the radiation center axis Cr is removed from the center of the width of the detection surface Sr of the radiation image detector 15 to the anode side so that the radiation bundle φH is on the region SSr along the detection surface Sr. , The detection surface Sr is irradiated with a radiation bundle portion φHBp which is a cathode side portion in the radiation bundle φH. The radiation intensity distribution in the radiation bundle portion φHBp is substantially constant because it contains many radiation bundles belonging to the cathode side that are less affected by the heel effect. That is, the radiation bundle portion φHBp that contains more radiation generated on the cathode side than the radiation generated on the anode side of the tube and the radiation bundle portion φHAp that includes radiation generated on the anode side of the tube and radiation generated on the cathode side equally. The effect of the heel effect is less than that.

  Since the direction of the tube 10K is changed by the tube swinging portion 19, a radiation bundle portion φHBp having a small irradiation unevenness due to the heel effect among the radiation bundle φH emitted from the tube 10K can be irradiated to the detection surface SSr. The imaging width and the like can be determined on the assumption that the radiation bundle portion φHBp is irradiated to each area in the subject M in each radiography.

  When performing radiography, unnecessary radiation is blocked by the collimator 12 included in the radiation source 10 so that the area other than the area in the subject M corresponding to the imaging width to be imaged in each radiography is not exposed. It is desirable.

  In addition, it is desirable to determine the shooting width so that adjacent image portions representing each area in the subject M share the same area in the subject M. That is, it is possible to more easily combine a plurality of image parts by obtaining each image part so that a part of adjacent image parts overlaps (by securing a margin area). it can.

  Note that, as described above, the imageable width acquisition unit 84 determines the imageable width to be smaller as the focal spot size of the tube is smaller, for example. In addition, when using the anode side radiation bundle, the imageable width acquisition unit 84 uses the size of the imageable width when applying tungsten to the tube target, and when applying molybdenum to the tube target. It is determined to be smaller than the shootable width. Further, the imageable width acquisition unit 84 determines the imageable width as the radiation dose increases, and determines the imageable width as the image distance decreases.

  Further, in the above-described embodiment, the radiographic imaging apparatus that performs long imaging in a standing position has been described. However, the present invention is not limited to this, and can also be applied to a radiographic imaging apparatus that performs long imaging in a prone position.

  As described above, according to the present invention, it is possible to easily acquire a high-quality long radiographic image in which the density step of the joint is not conspicuous.

DESCRIPTION OF SYMBOLS 10 Radiation source 15 Radiation image detector 82 Imaging condition acquisition part 84 Imaging | photography possible range acquisition part 86 Allocation part M Subject

Claims (7)

Using the same radiation source and the same radiation image detector, a long radiation that represents the entire subject by combining a plurality of images obtained by sequentially radiographing a plurality of adjacent regions in the subject. A radiographic imaging device for obtaining an image,
Imaging condition acquisition means for acquiring imaging conditions for each radiation imaging,
An imageable range acquisition means for obtaining an imageable width in the longitudinal direction in each radiography from the imaging conditions;
Allocating means for allocating a plurality of areas in the subject to be imaged so that an imaging width in the longitudinal direction in each radiography is equal to or less than the imageable width ,
The imageable range acquisition means is configured to obtain the imageable width when each region in the subject is irradiated with a radiation bundle portion having the smallest irradiation unevenness due to a heel effect among radiation bundles emitted from a tube of the radiation source. What is required is a radiographic imaging apparatus.   The radiographic image capturing apparatus according to claim 1, wherein the imaging condition is an imaging distance.   The radiographic image capturing apparatus according to claim 1, wherein the imaging condition is a dose of radiation emitted from a radiation source.   The radiographic image capturing apparatus according to claim 1, wherein the imaging condition is a focal spot size of a tube of the radiation source.   The radiographic image capturing apparatus according to claim 1, wherein the imaging condition is a material of a tube target of the radiation source. 6. The radiographic image capturing apparatus according to claim 5 , further comprising tube swinging means for changing the direction of the tube of the radiation source. Using the same radiation source and the same radiation image detector, a long radiation that represents the entire subject by combining a plurality of images obtained by sequentially radiographing a plurality of adjacent regions in the subject. A radiographic imaging method for obtaining an image,
Obtaining radiographic imaging conditions;
In each radiation imaging, a radiation bundle part having the smallest length of irradiation unevenness due to the heel effect among the radiation bundles emitted from the tube of the radiation source, which is an imageable width in the longitudinal direction, is irradiated to each region in the subject. Obtaining the imageable width at the time of shooting from the shooting conditions,
A radiographic imaging method, comprising: allocating a plurality of regions in the subject to be imaged so that an imaging width in the longitudinal direction in each radiography is equal to or less than the imageable width.